Plugin support for dynamic context (#783)

* Introduce a new plugin type: dynamic context labels.

* Test dynamic context plugins

* Helper method to get full paths to measured files

* Get correct filenames on all OS

* Improve wording

1 files changed, 10 insertions, 0 deletions

diff --git a/coverage/plugin_support.py b/coverage/plugin_support.py
index 0727a3b0..7c25a5f1 100644
--- a/coverage/plugin_support.py
+++ b/coverage/plugin_support.py
@@ -21,6 +21,7 @@ class Plugins(object):
         self.names = {}
         self.file_tracers = []
         self.configurers = []
+        self.context_switchers = []
 
         self.current_module = None
         self.debug = None
@@ -70,6 +71,15 @@ class Plugins(object):
         """
         self._add_plugin(plugin, self.configurers)
 
+    def add_dynamic_context(self, plugin):
+        """Add a dynamic context plugin.
+
+        `plugin` is an instance of a third-party plugin class.  It must
+        implement the :meth:`CoveragePlugin.dynamic_context` method.
+
+        """
+        self._add_plugin(plugin, self.context_switchers)
+
     def add_noop(self, plugin):
         """Add a plugin that does nothing.